Angiogenin (ANG) is a 14 kDa angiogenic ribonuclease that is upregulated in a variety of human cancers. Loss-of-function mutations in the coding region of ANG have recently been found in patients with amyotrophic lateral sclerosis (ALS). Studies carried out in the previous funding period have demonstrated an important role of ANG in ribosomal RNA (rRNA) synthesis, which is essential for many fundamental biological processes including cell growth, proliferation, and survival. We have created conditional Ang1 knockout mice and have shown that Ang1 null mice have reduced angiogenic response and increased susceptibility to stress-induced apoptosis. Mechanistically, we have demonstrated that the biological activity of ANG relies on its subcellular destination. Under growth condition, ANG is translocated to the nucleus where it stimulates ribosomal RNA (rRNA) transcription and processing thereby promoting cell growth and proliferation. Under stress, ANG is translocated to the stress granules where it enhances the production of tiRNA (tRNA-derived, stress-induced small RNA) that reprogram protein translation thereby promoting cell survival. We have also identified PlexinB2 as a functional ANG receptor that is both necessary and sufficient for mediating biological activity of ANG. We have shown that ANG and Semaphorin 4C (Sema4C), the other ligand of PlexinB2, bind at non-overlapping regions and trigger different signals. The objective of this proposal is to understand the mechanism of action of ANG in stimulating angiogenesis and cancer progression. This objective will be achieved by addressing the following four specific aims. (1) Assess the therapeutic activity of anti-ANG receptor (PlexinB2) antibody. We will examine the effect of anti-PlexinB2 monoclonal antibodies on angiogenesis and tumor progression in both xenograft and transgenic animal models. (2) Characterize the differential effect of ANG and Sema4C in angiogenesis and tumor progression. We will assess the effect of knockdown PlexinB2 and Sema4C on Akt- induced prostate intraepithelial (PIN) and compare the results with that from ANG knockdown. (3) Determine the role of ANG in stress-regulated protein translation and cell survival. We will identify the signals that direct translocation of ANG into stress granules and into nucleus. We will also characterize the role of ANG-mediated tiRNA in reprogramming protein translation and promoting cell survival. (4) Characterize the effect of Ang1 knockout and ANG overexpression in angiogenesis and tumor growth. We will examine the function of ANG in cancer susceptibility to oncogenic insults inflicted by environmental and genetic factors. We will also study autocrine vs. paracrine action of ANG and their respective contributions toward tumor angiogenesis and cancer cell proliferation. We anticipate that the results of these experiments will elucidate how ANG interacts with its cell surface receptor, how the signaling pathway is transduced, and how ANG promotes cell survival and proliferation. These results will provide a comprehensive understanding of the function and mechanism of ANG in angiogenesis and in cancer progression. PUBLIC HEALTH RELEVANCE: Angiogenin plays multiple roles in cancer progression by stimulating cancer cell proliferation and tumor angiogenesis, as well promoting cell survival. Previous studies have shown that angiogenin serves as a molecular target for cancer drug development. The goal of this proposal is to understand the mechanism by which angiogenin mediates angiogenesis and cancer progression.